Dependence of Charge Transport on the Degree of Ordering in Semicrystalline Conjugated Polymers

Abstract

The influence of ordering inside the crystalline regions of semi-crystalline polymer thin films on charge transport is investigated by analyzing the electric field dependence of mobility calculated using Monte Carlo simulation. The degree of ordering inside the ordered regions is varied by changing the overlap between the hopping transport sites. Negative field dependence of mobility extending to higher electric field strengths along with an increase in the mobility are observed upon increasing the overlap between transport sites inside the ordered region. These observations are attributed to the variation in the charge transport, which affects the transit time that not only decreases but also shows a gradual shift from negative to positive field dependence at lower electric field strengths (∼<3 × 10⁵ V/cm). Variations in the transit time are explained using the variation in the field dependence of hops performed by the carrier inside the ordered and disordered regions. Field dependence of mobility is also simulated with ballistic charge transport inside the ordered regions. At low concentrations of ordered regions (COR), higher carrier mobility is attained with hopping transport (∼<70%). Ballistic transport provides higher mobility at higher COR (∼>70%). This suggests that a very high order inside the ordered region may not necessarily provide higher mobility.